<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>旋转的星空</title>
<style type="text/css">
body{background: black;padding: 0;margin: 0; overflow:hidden}
.header{margin: 0 auto;width: 100%;height: 100%;background-color: #000;position: relative;}
</style>
</head>
<body>
<div class="header"><canvas id="canvas"></canvas></div>
<script>
var canvas = document.getElementById('canvas'),
ctx = canvas.getContext('2d'),
w = canvas.width = window.innerWidth,
h = canvas.height = window.innerHeight,
hue = 217,
stars = [],
count = 0,
maxStars = 3000;//星星数量
var canvas2 = document.createElement('canvas'),
ctx2 = canvas2.getContext('2d');
canvas2.width = 100;
canvas2.height = 100;
var half = canvas2.width / 2,
gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
gradient2.addColorStop(0.025, '#CCC');
gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
gradient2.addColorStop(1, 'transparent');
ctx2.fillStyle = gradient2;
ctx2.beginPath();
ctx2.arc(half, half, half, 0, Math.PI * 2);
ctx2.fill();
// End cache
function random(min, max) {
 if (arguments.length < 2) {
max = min;
min = 0;
 }
 if (min > max) {
 var hold = max;
max = min;
min = hold;
 }
 return Math.floor(Math.random() * (max - min + 1)) + min;
}
function maxOrbit(x, y) {
 var max = Math.max(x, y),
diameter = Math.round(Math.sqrt(max * max + max * max));
 return diameter / 2;
 //星星移动范围，值越大范围越小，
}
var Star = function() {
 this.orbitRadius = random(maxOrbit(w, h));
 this.radius = random(60, this.orbitRadius) / 8;
 //星星大小
 this.orbitX = w / 2;
 this.orbitY = h / 2;
 this.timePassed = random(0, maxStars);
 this.speed = random(this.orbitRadius) / 50000;
 //星星移动速度
 this.alpha = random(2, 10) / 10;
count++;
stars[count] = this;
}
Star.prototype.draw = function() {
 var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
twinkle = random(10);
 if (twinkle === 1 && this.alpha > 0) {
 this.alpha -= 0.05;
 } else if (twinkle === 2 && this.alpha < 1) {
 this.alpha += 0.05;
 }
ctx.globalAlpha = this.alpha;
ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
 this.timePassed += this.speed;
}
for (var i = 0; i < maxStars; i++) {
 new Star();
}
function animation() {
ctx.globalCompositeOperation = 'source-over';
ctx.globalAlpha = 0.5; //尾巴
ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
ctx.fillRect(0, 0, w, h)
ctx.globalCompositeOperation = 'lighter';
 for (var i = 1, l = stars.length; i < l; i++) {
stars[i].draw();
 };
window.requestAnimationFrame(animation);
}
animation();
</script>
</body>
</html>